Signal analyzer and method for displaying power levels of code channels

ABSTRACT

A signal analyzer and a method for displaying code-channel power levels of CDMA (Code Division Multiple Access) signal that contains code changes having different spreading factors. The individual code-channel power level is measured from a received signal and displayed in a diagram for a specified base spreading factor. The code channels having an alias power level are indicated. A code channel, with regard to the specified base spreading factor, has an alias power level when the code channel having the base spreading factor is inactive and when a code channel of a higher spreading factor (corresponding to the former code channel) is active, or, in the event of orthogonal transmit diversity, the power level of a code channel is mapped onto the code channel of the base spreading factor.

FIELD OF THE INVENTION

The invention relates to a signal analyzer and a method for displayingthe power level of code channels of a CDMA (Code Division MultipleAccess) signal.

BACKGROUND OF THE INVENTION

In the context of checking the components of third-generation mobiletelephone systems, it is necessary to determine the power level of theindividual code channels, of which the overall signal is made up. Therelevant power levels of the code channels are presented graphically toevaluate the measured power levels of the individual code channels. Agraphic presentation of this kind of the power levels of individual codechannels is disclosed, for example, in U.S. Pat. No. 6,219,340 B1.

According to U.S. Pat. No. 6,219,340 B1, the individual power levels ofthe relevant active code channels are presented in the form of a bardiagram. In this diagram, the individual channels are plotted along theX-axis in such a manner that the code channels belonging to each codeclass are arranged adjacent to one another. The power level measured foreach code channel is shown by the height of the bar. The membership ofthe individual code channels in a given code class, that is to say,their association with a given spreading factor (SF), is shown, in thepresentation proposed, in that, corresponding to the lower spreadingfactor in the lower code class, the bar allocated in the presentation iswider for the corresponding code channel of the lower code class.Moreover, U.S. Pat. No. 6,219,340 B1 proposes that inactive codechannels are indicated in the presentation by a dash. In this context,inactive channels are understood to be all code channels, which do notcontribute to the data transmission.

The presentation of a measured CDMA signal proposed in U.S. Pat. No.6,219,340 B1 has the disadvantage that it is not possible to distinguishwhether a code channel in a code class is actually active, or whetherthe code channel is inactive but the power level of a corresponding codechannel of a higher spreading factor is measurable there. A lack ofdiscrimination of this kind between an actual power level of an activecode channel and a so-called alias power level of an inactive codechannel in a code class, which is lower than the actual code class ofthe active code channel, considerably impairs the evaluation of theoverall CDMA signal.

SUMMARY OF THE INVENTION

There exists a need to create a signal analyser and a method fordisplaying the code-channel power levels of a CDMA signal, wherein adistinction can be made between a power level, which actually originatesfrom an active code channel, and an alias power level.

According to one aspect of the invention, those code channels relatingto a specific base spreading factor which are inactive, but for which aso-called alias power level occurs, are specially marked in a diagram,which presents the power levels occurring in the individual codechannels. In evaluating the individual power levels of the codechannels, it is therefore possible to distinguish simply betweenactually active code channels and code channels, which are inactive inthe specified base spreading factor. This distinction is also possible,if the actually inactive channels show a measurable power level in theform of an alias power level.

In particular embodiments, it is advantageous to select a bar diagramfor the presentation of the power level of the individual code channels,and to present those bars of the code channels, in which an alias powerlevel is measurable, in a different color. With this color marking, itis possible to infer simply from the diagram which code channels providean alias power level, which actually originates from code channels of ahigher code class. In this way, the information regarding the level ofthe power level actually measured is retained.

Moreover, it is particularly advantageous, in the event of an occurrenceof an alias power level of this kind, to switch automatically, inresponse to an entry by an operator, to the presentation of that codeclass, which contains the code channels causing the alias power level.Starting from a presentation of the code class with the basic spreadingfactor, the operator can then immediately recognise the code class, fromwhich the alias power level occurring in a lower code class actuallyoriginates. A further simplification is possible if, when switching to apresentation with a higher spreading factor, the code channel, whichshows an alias power level, is marked with a marking device, which isallocated to the corresponding code channel causing the alias powerlevel.

With another marking, for example, a differently colored marking, it isalso possible, when using several antennae of the same transmissionunit, to which mutually orthogonal codes are allocated, to distinguishwhether the alias power level originates from a signal of the sameantenna or from a code channel of the other antenna. The use ofdifferent markings for code channels, which provide alias power levelsof different origins, allows the corresponding causes for the aliaspower level to be distinguished in a simple manner.

Still other aspects, features, and advantages of the present inventionare readily apparent from the following detailed description, simply byillustrating a number of particular embodiments and implementations,including the best mode contemplated for carrying out the presentinvention. The present invention is also capable of other and differentembodiments, and its several details can be modified in various obviousrespects, all without departing from the spirit and scope of the presentinvention. Accordingly, the drawing and description are to be regardedas illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

One preferred exemplary embodiment of the invention is presented in thedrawings and explained in greater detail below. The drawings are asfollows:

FIG. 1 shows a schematic presentation of the occurrence of an aliaspower level;

FIG. 2 shows a presentation of measured power levels of code channelswith an alias power level for a base spreading factor;

FIG. 3 shows a presentation of the power levels of the code channelsfrom FIG. 2 for a higher spreading factor;

FIG. 4 shows a schematic presentation of the occurrence of an aliaspower level through the use of two antennae;

FIG. 5 shows a presentation of the power levels of the code channels fora base spreading factor in a bar diagram;

FIG. 6 shows a presentation of the power levels of the code channelsfrom FIG. 5 for a higher spreading factor;

FIG. 7 shows a further schematic presentation of the occurrence of analias power level and

FIG. 8 shows a block circuit diagram of a signal analyzer according tothe invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With a third-generation mobile telephone system, a base stationcommunicates with several mobile devices, the various mobile stationstransmitting information simultaneously to the base station and viceversa. The individual signals sent to or from the mobile stations aredistinguished by allocating corresponding codes to the subscribers, thecorresponding codes being mutually orthogonal. The number of items ofinformation to be transmitted per unit of time can be varied independence upon the spreading factor SF, upon which the code is based.To exploit the transmission capacity to the maximum, the signal actuallyreceived and/or transmitted by the base station consists of codechannels, which provide different spreading factors.

Each code of a given spreading factor branches again in the plane of thenext higher spreading factor into two orthogonal codes. FIG. 1illustrates this by way of example for the code 4 with a spreadingfactor 64 (reference C4). In the next higher code class, that is, with aspreading factor 128, the code 4 is subdivided into a code 4 withspreading factor 128 (reference C4′) and a code 68 with the spreadingfactor 128 (reference C68). FIG. 1 shows a detail of a code tree diagramwith three code classes with the spreading factors 64, 128 and 256respectively.

The code 32 relating to spreading factor 64 (C32), shown schematicallyin FIG. 1 with dark shading, and code 68 relating to spreading factor128 (C68) are active. When measuring the signal with the assistance of asignal analyser, which presents each measured power level of the codechannels relating to the spreading factor 64, the power level of theactive code channel 32 is presented with an additional power level forthe code channel 4. In this context, the power level of the code channel4 is a so-called alias power level, which also occurs with an inactivecode channel 4 and originates from an actually active code channel 68 ofthe spreading factor 128. The code channel 4 of the spreading factor128, however, is actually inactive. In the diagrams, inactive codechannels are represented by empty circles.

FIG. 2 shows a presentation of the power levels of the individual codechannels for the basic spreading factor 64. In this presentation as abar diagram, the individual code channels are plotted horizontally, sothat the height of the bars allocated to the individual code channelsindicates the measured power level for each code channel. Code channels,which are actually active in the code class presented are marked withthe reference 2 in FIG. 2 and are presented, for example, in a givencolor. The code channels, which are inactive with a basic spreadingfactor of 64 are preferably presented in another color and are shown inFIG. 2 by way of example with the reference 3.

As already explained in the context of FIG. 1, the code channel C4,which provides an alias power level, is labelled with the reference 5 inFIG. 2 and is marked in a special manner by the display device 1. Forexample, with the bar diagram selected in FIG. 2, a differently coloredbar may be used for this purpose. Furthermore, a marking 4 is shown inFIG. 2, which can be allocated by the operator of the measuring deviceto any desired code channel. In the example presented, the marking 4 isallocated to the color-marked code channel C4 (reference 5).

FIG. 3 provides a presentation of the measured results, as already shownin FIG. 2, for a spreading factor 128, that is to say, for the nexthigher code class. As already explained in the context of FIG. 1, in thepresentation relating to the spreading factor 128, an unambiguousdistinction must be made between the code channel C68 and the codechannel C4′. Accordingly, the display device 1 displays only a slightnoise power level for the code channel C4′ labelled with the reference5′, which is synonymous with the statement that the code C4′ is actuallyinactive. By contrast, a relatively high power level is indicated forthe code channel C68 labelled with the reference 5″, which means thatthe code channel C68 is actually active and has therefore caused thealias power level of the code channel C4 with spreading factor 64. Sincethe code channel C68 provides an actual power level rather than an aliaspower level, the bar allocated to the code channel C68 is now no longermarked with a special color. On the contrary, it is shown with the samecolor as all other active code channels relating to the spreading factor128. To make it easier to locate the corresponding code channel, themarking 4 from FIG. 2 is set as the marking 4′ on the code channel C68in FIG. 3. This displacement of the marking 4, 4′ corresponds to theoccurrence of the alias power level on the basis of the code generationaccording to the Hadamard matrix.

Other presentations are also possible instead of the preferredpresentation in a bar diagram with special coloring of the correspondingcode channels, for example, arrow diagrams or line diagrams etc. It isalso possible to mark a code channel, which provides an alias powerlevel, by other means than coloring. For example, shading, a borderarranged around the bar, a flashing bar or arrow may be considered.

FIG. 4 presents a further possibility for the occurrence of the aliaspower level, as it arises in transmission units with two antennae,wherein the antennae each use codes, which are mutually orthogonal(Orthogonal Transmit Diversity OTD)). In this context, the channels of afirst antenna ANT1 and a second antenna ANT2 are each spread with anadditional orthogonal spreading factor. This means that the codechannels are actually disposed in a plane of the code tree diagram witha doubled spreading factor.

In FIG. 4, this is shown by way of example for the code channel 16 ofantenna ANT1 with spreading factor 64. As indicated by the empty circle,the code channel C16′ of the antenna ANT1 with spreading factor 128 andOrthogonal Transmit Diversity is inactive. The code channel C144 (Code16, antenna ANT2, spreading factor SF128 with OTD), however, is active.Accordingly, the power level of the code channel C144 is measured as thealias power level of the code channel C16 (Code 16, antenna ANT1,spreading factor SF64 with OTD). A corresponding presentation on adisplay device 1 is again shown in FIG. 5, for a basic spreading factor64. The only-apparently-active code channel C16 is labelled in FIG. 5with reference 6 and highlighted by the use of another color in the bardiagram. The marker 7, allocated in FIG. 5 to the code channel C16, isagain, in the presentation relating to the spreading factor 128 shown inFIG. 6, allocated to the code channel C16′, which does not now providean alias power level and is accordingly shown as inactive. In thepresentation shown, all code channels belonging to the antenna ANT1 arepresented in such a manner that the code channel causing the alias powerlevel is not recognisable.

FIG. 7 shows, by way of example, the occurrence of an alias power levelthrough the active code channels of a higher code class and simultaneoususe of Orthogonal Transmit Diversity. In code channel 18 in this diagram(Code 18, antenna ANT1, spreading factor SF64 with OTD), a power levelwith the next higher spreading factor, which originates from codechannel 18 of the next code class (antenna ANT1, spreading factor SF128)with Orthogonal Transmit Diversity, can be identified, and also a powerlevel, which originates from code channel 18 of antenna ANT2 withspreading factor 128 with OTD. Both power levels are mapped in the codechannel C18 of the antenna ANT1 with spreading factor SF64 withOrthogonal Transmit Diversity and accordingly marked in color in adiagram, which presents the power level distribution of the individualcode channels, wherein the marking corresponds, preferably in dependenceupon the application, either to the marking of alias power levels of ahigher code class or of alias power levels through OTD.

FIG. 8 shows a schematic presentation of a signal analyser according tothe invention. The signal analyser 10 according to the invention has aninput connection 11, to which a CDMA signal 12 to be measured isconnected. The input connection may be either an antenna connection forthe antenna 18 or a connection for a signal line. The incoming signal 12is supplied from the input connection 11 to an analysis device 13. Inthe analysis device 13, the incoming CDMA signal is analysed, so thatthe actual power level is determined for all active code channels andaccordingly, the active code channels can be allocated to the codeclasses. To display the measured power level of the individual codechannels on a display device 14, an entry is implemented by the operatorin an operating field 15, which is supplied via a connection 16 to theanalysis device. The presentation parameters entered in the operatingfield 15 contain, for example, the selection of specified base spreadingfactors for the display.

The power levels of the code channels to be presented for a specifiedbase spreading factor are communicated by the analysis device 13 via afurther connecting line 17 to the display device 14, on which, onceagain, the measured power levels of the individual code channels aredisplayed in a presentation corresponding to the presentation from FIG.2, FIG. 3, FIG. 5 and/or FIG. 6.

If the operator recognises, on the basis of the color presentation ofcode channels, that a code channel provides an alias power level, he canmake an entry via the operating field 15, in response to which, theanalysis device 13 communicates to the display device 14 the informationrequired for a modified presentation of a higher code class with thecorresponding higher spreading factor SF. A presentation relating to thesmallest spreading factor, for which no alias power level occurs in thecode channels, can also be selected automatically. The presentation fora given spreading factor can also be selected directly via the entry,instead of an automatic switching of the presentation relating to aspreading factor.

Furthermore, FIG. 8 illustrates the case, in which a transmitter 19transmits via two generally spatially offset antennae ANT1 and ANT2,wherein the codes used are spread into the next higher code class, asdescribed above.

While the present invention has been described in connection with anumber of embodiments and implementations, the present invention is notso limited but covers various obvious modifications and equivalentarrangements, which fall within the purview of the appended claims.

1. A method for displaying power levels of code channels of a CDMA (Code Division Multiple Access) signal, said code channels having different spreading factors, comprising: receiving the CDMA signal; measuring the power levels of the code channels of the CDMA signal; displaying the measured power levels of the code channels for a specified base spreading factor in a diagram; and marking those code channels, which provide an alias power level, wherein a code channel provides an alias power level relating to the specified base spreading factor when the code channel with the specified base spreading factor is inactive, and a code channel of a higher spreading factor corresponding thereto is active, when measuring a CDMA signal from a transmitter with a first antenna and a second antenna, which use mutually orthogonal codes, marking a code channel with the spreading factor of the first antenna, in which an alias power level occurs, which is an actual power level of an active code channel of the second antenna, differently from a code channel with an alias power level, which is an actual power level of a code channel with a higher spreading factor of the same antenna.
 2. A method according to claim 1, wherein the power levels of the code channels are displayed in a bar diagram.
 3. A method according to claim 1, wherein those code channels which provide an alias power level, are marked in color.
 4. A method according to claim 1, further comprising automatically displaying the power levels of the code channels after a user entry, with the highest spreading factor that contains an active code channel.
 5. A method according to claim 1, further comprising: assigning a marking allocated to a code channel providing an alias power level, in the case of a change to a higher spreading factor, to a code channel causing the alias power level.
 6. A signal analyzer for measuring a plurality of power levels of respective code channels of a CDMA (Code Division Multiple Access) signal, comprising: an analysis device for evaluating the power level of the individual code channels; and a display device for visual presentation of the power levels of the individual code channels of a given basic spreading factor in a diagram, wherein those code channels relating to the specified base spreading factor, which are inactive and for which an alias power level is measurable, are marked in the diagram, an alias power level being present, if a code channel of a higher spreading factor, which corresponds to an inactive code channel relating to a specified base spreading factor, is active, wherein in analyzing a CDMA signal of a transmitter with a first antenna and a second antenna, which use mutually orthogonal codes, those code channels of an antenna, for which an alias power level is measurable, which is caused by an active code channel of the other antenna, are presented differently from code channels with a measurable alias power level, which is caused by an active code channel of a higher spreading factor of the same antenna.
 7. A signal analyzer according to claim 6, wherein the power levels of the code channels is presented in a bar diagram.
 8. A signal analyzer according to claim 6, wherein the inactive code channels of the specified base spreading factor, for which an alias power level is measurable, are marked in the diagram in a different color from the active code channels of the specified base spreading factor.
 9. A signal analyzer according to claim 6, wherein the code channels relating to the maximum spreading factor, which contains an active code channel, are automatically presented on the display device. 